Nanotechnology in action: overbased nanodetergents as lubricant oil additives.

The synthesis and study of oil-soluble metal carbonate colloids are of interest in the area of lubricant additives. These surfactant-stabilised nanoparticles are important components in marine and automotive engine oils. Recently introduced, environmentally driven legislation has focused on lowering of gaseous emissions by placing limits on the levels of phosphorous sulphur and ash allowed in engine oil systems. These chemical limits, coupled with improved engine performance and extended oil drainage intervals, have lead to renewed interest in the production of stable, efficient nanodetergent systems. To date, this has resulted in modification of existing surfactant structures and development of new generations of surfactants. This review covers the current state of research in the area of nanodetergents.

Interactions between a nonionic gemini surfactant and cyclodextrins investigated by small-angle neutron scattering.

The microstructure of complexes between hydroxypropyl-cyclodextrins (HPCDs) (alpha, beta, and gamma) and a novel gemini surfactant has been investigated by small-angle neutron scattering (SANS). This nonionic hetero-gemini surfactant (denoted NIHG750) contains two hydrophobic groups and two hydrophilic groups. One is a methyl-capped polyoxyethylene chain with 16 oxyethylene units and the other is a secondary hydroxyl group. Various form factor models have been considered for fitting the SANS data. Spherical aggregates (25 to 40 A) with a size slightly larger than that of NIHG750 micelles (about 23 A) appear in mixed systems. These could be micellar aggregates partly covered with a few cyclodextrin molecules. In addition, the results indicate rod formation (r approximately 8 A, L approximately 70 A) for the NIHG-HPCD complexes. This result is consistent with the threading of HPCDs onto NIHG750 to such an extent that the surfactant molecule takes an extended conformation at high levels of HPCD. Also, the results indicate that HPCDs may interact with the oxyethylene groups of the spherical micellar aggregates leading to an increase in micelle size and a gradual transformation to rod-shaped aggregates. The tendency to form rods increases in the order gamma-CD

Interaction between a novel gemini surfactant and cyclodextrin: NMR and surface tension studies.

The interaction between cyclodextrins, hydroxypropyl-beta-cyclodextrin (HPbetaCD), and hydroxypropyl-gamma-cyclodextrin (HPgammaCD) and a novel type of nonionic surfactant synthesized from a fatty acid has been investigated. The so-called nonionic heterogemini surfactant (NIHG750) contains two hydrophobic groups and two hydrophilic groups, composed of one monomethyl ethylene glycol and one secondary OH group, CH(3)(CH(2))(7)-CH[OH]-CH[O(CH(2)CH(2)O)(16)CH(3)]-(CH(2))(7)CN. Surface tension studies indicate that micelles form in NIHG750 systems in both the presence and the absence of small quantities (molar ratio (HPbetaCD:NIHG750) approximately 2) of cyclodextrin (HPbetaCD or HPgammaCD). This gives NIHG surfactants an advantage compared to single-tailed nonionic surfactants, which generally lose their ability to micellize at much lower additions of cyclodextrins. However, the interaction between HPbetaCD and NIHG750 results in a disruption of the micellar aggregates at higher levels of cyclodextrin. In the dilute systems (C(NIHG750)<0.1% (w/w) approx) prolate-shaped mixed aggregates (HPbetaCD and NIHG750) form, with a short and a long axis of the order of 8-9 and 17-20 A, respectively. These gradually aggregate into micellar-like structures at higher concentrations. In the aqueous bulk phase HPbetaCD interacts mainly with the hydrophobic part of NIHG750, but both NMR and surface tension measurements indicate that an interaction with the hydrophilic part of NIHG750, as well, may exist. This interaction results in a better packing of NIHG750 at air-water interfaces. However, at elevated temperatures results from turbidity measurements indicate that NIHG750 and HPbetaCD interact mainly through the hydrophilic part of the surfactant; a decrease in the cloud point temperature is observed. The interaction of the larger cavity molecule, HPgammaCD, with NIHG750, on the other hand, seems to be relatively weak. The interaction, when present, most probably takes place through inclusion of the hydrophilic EO part of NIHG750. The results suggest that HPgammaCD in combination with NIHG750 is a better solubilizing system than with HPbetaCD.

Adsorption properties of novel gemini surfactants with nonidentical head groups.

Novel environmentally friendly gemini surfactants, each with two hydrophilic and two hydrophobic groups, have been synthesized and their physicochemical properties investigated. One of the hydrophilic groups is a methyl-capped polyoxyethylene chain with mol wt 350, 550, and 750 g/mol, respectively, and the other is a sulfate group; the hydrophobic part of the surfactant is made from oleylnitrile. This nitrile derivative of the fatty acid is used to achieve good hydrolytic stability. Du Nouy ring and maximum bubble pressure tensiometry were used for equilibrium and dynamic surface tensions, gamma(e) and gamma(t), respectively. The aqueous-phase critical micelle concentrations of the heterogeminis (HGs) have been investigated. The results have been compared with those for mixtures of standard surfactants sodium decylsulfate and octaoxyethyleneglycol mono n-decyl ether under equivalent conditions. The HGs are shown to exhibit improved performance over the mixed system both in terms of micellization and surface tension lowering. Dynamic surface tension (DST) studies were performed to investigate air-water adsorption mechanisms. A diffusion-limited mechanism was confirmed in the initial stages of adsorption. However, closer to the equilibrium the DST data are inconsistent with a diffusion-only mechanism. In particular, the HGs show a larger deviation from diffusion control as compared to the model mixture, which is a signature of slower adsorption kinetics. In addition to air-water interfaces, properties of these HGs have also been investigated at solid silica-solution surfaces by optical reflectometry. These surfaces were either naturally hydrophilic or rendered hydrophobic by chemical modification. On either surface the maximum amount of adsorbed surfactant was found to increase when the polyoxyethylene chain length decreases.

Dynamic surface tension and adsorption mechanisms of surfactants at the air-water interface.

Recent advances in understanding dynamic surface tensions (DSTs) of surfactant solutions are discussed. For pre-CMC solutions of non-ionic surfactants, theoretical models and experimental evidence for a mixed diffusion-kinetic adsorption mechanism are covered. For micellar solutions of non-ionics, up to approximately 100 x CMC, the DST behaviour can also be accounted for using a mixed mechanism model. Finally, the first reported measurements of the dynamic surface excess Gamma(t), using the overflowing cylinder in conjunction with neutron reflection, are described.

Microemulsions with Didodecyldimethylammonium Bromide Studied by Neutron Contrast Variation

The structure of water-in-oil microemulsion droplets, stabilized by didodecyldimethylammonium bromide (DDAB), has been investigated by small-angle neutron scattering (SANS). Detailed information about the curved surfactant film has been obtained by selectively deuterating the water, DDAB, and cyclohexane components. For each surfactant h -DDAB and d -DDAB and concentration, three sets of complementary neutron contrast data were analyzed together in terms of a Schultz distribution of core-shell particles. The modeling was consistent with a simple liquid-like surfactant layer, of density 0.80 g cm-3 , with no evidence for any solvent penetration. This film thickness was found to be 11-12 A, about 70% of an all-trans C12 chain length. At the water interface the area per head was 56-61 A2 , while for the alkyl chains at the outer surface it was 90-125 A2 (15-30% lower than that for a truncated cone molecular configuration). The cyclohexane-water interfacial tensions gammao/w , measured by surface light scattering, were used along with the droplet polydispersities to find that the rigidity of the DDAB film, 2K + K ; is close to 1.0k B T . This means that rather than acting as an effective parameter in the SANS analysis, the polydispersity is a natural consequence of the film rigidity. These results show that the film bending energy model accounts well for the behavior of such DDAB microemulsions.

Some influences on the measurement of food intake during a dietary survey of adolescents.

Data are presented from a recent longitudinal study of dietary habits of English children aged 11-13 y, in relation to various factors which may have influenced the estimations of intake. A knowledge of such relationships may aid the design and interpretation of this and other dietary surveys. The factors studied included survey fatigue, learning effect, season of the year, day of the week and the subjects' knowledge of the study's purpose. Generally the relationships found were of minor importance, but the variable influence of some of these factors is apparent from a study of the relevant literature. This is one reason why dietary survey methodology is resistant to simplification. It is concluded that the dietary survey method used was adequate for the purpose of the study.

A two-year longitudinal study of dietary intake in relation to the growth of 405 English children initially aged 11-12 years.

This report is of a two-year longitudinal study of dietary intake and growth in height and weight of 405 children, initially aged 11-12 years. Between 1979 and 1981 they each recorded their food intake on five occasions for three consecutive days using a diet diary with a 20 min private interview on the fourth day. Computerized food tables were used. Social class was recorded. The usual differences in height, weight and growth increments between the social classes were found. There were no significant differences in nutrient intake between social classes. Within a social class there were few statistically significant correlations between energy or protein intake and height or weight increments. It was concluded that a very high reliability of food intake measurements would be required in order to relate diet to growth and many other factors (e.g. energy expenditure, body composition and puberty) may also mask any such relationship. Social class alone would seem an inadequate means of allowing for such factors.

Sugars-eating habits of 405 11- to 14-year-old English children.

Between September 1979 and July 1981, 405 northern-English children, initially aged 11-12 years, each recorded all food and drink consumed on five occasions on each of three consecutive days. Sugars and nutrient intakes were calculated using food tables. The average total sugars intake was 118 g/d or 21% of the energy intake and 43% of the carbohydrate intake; these percentages were similar for both sexes, all social class groups and surveys. Sugars were found to be derived from a variety of food sources with confectionery being the single largest source. Sugars were fairly evenly consumed over the average day with a high amount in foods eaten between meals. Snacks accounted for 65% of the sugars intake but only 46% of the energy intake. Sugars intake and snacking therefore seem to have been major components of the eating habits of these children. If dietary changes towards lower sugars intakes are to be achieved a vigorous, informed health education campaign is necessary together with effective labelling of manufactured foods, the development of new products and the modification of some existing ones.

The importance of fortification of flour with calcium and the sources of Ca in the diet of 375 English adolescents.

The contribution of the fortification of flour with calcium carbonate to the Ca intake of 375, 11-14-year-old Northumbrian children has been calculated. Mean Ca intakes were above those currently recommended for children of this age. The fortification of flour supplied 16% of the total Ca intakes. Without the fortification, the percentage of these children with intakes below the recommended intake would be more than double. This would include the majority of girls (particularly those of social classes III, IV and V). The recommendation to stop fortifying flour with calcium carbonate should be reviewed.

A 2-year longitudinal nutritional survey of 405 Northumberland children initially aged 11.5 years.

Children (405), initially of average age 11.5 years, recorded all food and drinks consumed for three consecutive days (with an interview on the fourth day) on five separate occasions over a 2-year period. Food tables (Paul & Southgate, 1978) enabled nutrient intakes to be calculated. The data collected were found to be of high reliability (Hackett et al. 1983). The mean energy intakes showed broad agreement with other recent British dietary surveys but were well below those recorded in the prewar study by Widdowson (1947) and the FAO/WHO (1973) recommended levels. They were slightly below the current Department of Health and Social Security (DHSS; 1979) recommended intakes. Over the 2-year period, the energy intake of the boys increased by 13% compared with an increase of only 7% in the girls. The iron and vitamin A intakes of all groups of children were low compared with current recommendations (DHSS, 1979). This seems to be a result of falling energy intake. Mean calcium intakes were also only marginally in excess of the recommended intake, and those of most of the girls would fall below the recommendation if the proposal to end the fortification of flour (DHSS, 1981) is implemented.

Relationship between dietary habits and caries increment assessed over two years in 405 English adolescent school children.

The study was conducted in seven schools on children initially aged 11.5 years. They recorded their diet on five occasions, each of three days, and received an annual dental examination, including radiography. Caries increments were low, mostly (58 per cent) in fissure surfaces. Correlations between caries increment and dietary factors were low due to the low caries increments observed and the large error associated with dietary data where analyses attempt to discriminate between individuals. The highest correlation was between caries increment and weight of daily intake of sugars (+0.143, p less than 0.01). Multivariate analyses revealed that this relationship could not be explained by differences in sex, social class, tooth-brushing habits or level of plaque as measured by gingival inflammation. Weight of sugar intake appeared to be more strongly correlated to caries than frequency of intake; concentration of sugars in foods was positively related, and sugars in snacks were more strongly related to caries than total dietary sugars. The 31 children who consumed most sugar (greater than 163 g/day) developed 5.0 DMFS during the 2 years, 0.9 DMFS per year more than the 31 children (3.2 DMFS during 2 years) who had the lowest sugar intake (less than 78 g/day).

Enamel protein chemistry--past, present and future.

Past progress in the chemistry of enamel proteins is reviewed and the current state of knowledge assessed. The matrix of young enamel is a complex system in which some 20 distinct components with molecular weights in the region of 3,000 to 16,000 are in dynamic equilibrium with much larger aggregates. During maturation, most of these components are selectively lost, more or less completely, from the enamel. 'Amelogenin' components rich in proline and histidine are removed first and 'tuft protein', characterized by high serine and glycine, is often partially retained in mature enamel. Some components have been isolated in a state approaching purity and a measure of agreement has been reached between laboratories concerning their characteristics. Partial amino acid sequences are known for two components, which contain phosphoserine. Though the mechanisms of mineralization and protein removal are not known, various possibilities are discussed. The essential unsolved problem is the nature of the overall protein system.